Power distribution system

ABSTRACT

A power distribution system to distribute electric power having a source of alternating current of a frequency of 10 kHz or greater, a distribution line connected to the source, and at least one load. The distribution line has two substantially flat conductors separated by an insulating sheet, and an element formed of a material of high relative permeability associated with at least one of the conductors. With use of the system an electronic ballast can be used with dichroic and discharge lamps, with high efficiency and absence of light flicker. Substantial reduction in H field interference due to the high frequency alternating current is achieved with use of the distribution line.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power distribution system and moreparticularly relates to a power distribution system adapted todistribute electric power from a power source to at least one load.

2. Description of Related Art

Various power distribution systems have been used to distribute powerfrom a power source to a load. The power may be distributed at a typical“mains” voltage of 240 volts (or, in some countries 110 volts) and at atypical “mains” frequency of 50 cycles per second (in some countries, 60cycles per second). A disadvantage of this type of distribution systemis that since a relatively low voltage is used, for a moderate powersupply, a substantial current flows, meaning that the conductors must becapable of carrying a substantial current. Consequently, the cablestypically include conductors formed of copper, the conductors having arelatively large cross-section.

If a distribution system of this type is utilized with a discharge lamp,for example, a step-up transformer has to be utilized. Since thefrequency of the alternating current is relatively low, the transformermust be relatively bulky.

There is a desire to be able to utilize, in connection with dichroiclamps and discharge lamps, an electronic ballast. An electronic ballastis small and light and also, in connection with a discharge lamp,provides high efficiency and a light that is substantially flicker-free.However, to be able to utilize an electronic ballast, there is a needfor a high frequency alternating current. In many states, locallegislation insists that where an electronic ballast is utilized, apower factor connector must be provided to ensure that the power factor“seen” at the main supply is appropriate. A problem exists in connectionwith a high frequency power distribution system in that substantial Hfield “interference” can be generated.

SUMMARY OF THE INVENTION

The present invention seeks to provide an improved power distributionsystem.

According to this invention there is provided an electric powerdistribution arrangement comprising a source of alternating currenthaving a frequency of 10 kHz or greater, and a distribution lineconnected to said source. The distribution line comprises three layersconstituted by: two conductors, each of substantially flatconfiguration, the conductors being located in spaced parallelism andbeing located a short distance apart; and, an insulator that separatesthe two conductors At least one of the conductors, included in the threelayers of the transmission line, being associated with a respectivefurther element formed of a material of high relative permeability. Thatfurther element comprising a foil secured to the face of the conductor,remote from the insulator. The arrangement further comprises at leastone load connected to said conductors to receive electric powertherefrom.

In one embodiment the load is connected directly to the two conductors.In another embodiment the load is connected to the conductors by meansof a transformer, the transformer having a primary winding connected tothe two conductors, and having a secondary winding connected to theload. It is conceivable that the load comprises a low voltageincandescent lamp, but preferably the load comprises a discharge lamp,an impedance being provided which is connected in circuit with thesecondary winding and the discharge lamp.

In another embodiment each load comprises a discharge lamp connected toone conductor of the distribution line by means of an inductance, andconnected directly to the other conductor of the distribution line.

Preferably the source of alternating current comprises a power factorcorrector, which receives supply from a mains electricity supply, and aninverter which receives power from the power factor corrector.

Conveniently the power factor corrector comprises a rectifier producinga DC output, the DC output of the power factor corrector being providedas an input to the inverter.

Advantageously a transformer is provided located between the source ofthe high frequency current and the distribution line.

Advantageously a second element of high permeability is providedassociated with the other conductor.

Conveniently each element of high relative permeability extendslaterally beyond the associated flat conductor.

Preferably each element of high permeability is formed of an amorphousor nano-crystalline metal.

Conveniently each conductor is of flat cross-section, with two opposedparallel flat faces. The insulator separating the conductors comprisinga sheet of insulating material.

Advantageously the foil is separated from the face of the conductor towhich it is secured by means of an insulating layer.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more readily understood, and so thatfurther features thereof may be appreciated, the invention will now bedescribed, by way of example, with reference to the accompanyingdrawings in which:

FIG. 1 is a view of a power transmission line suitable for use in apower distribution system in accordance with the invention, with partsthereof cut away for the sake of clarity of illustration,

FIG. 2 is a view corresponding to FIG. 1 illustrating a second powerline for use in the invention,

FIG. 3 is a view of a power transmission line for incorporating into thecircuit of a power generator in accordance with the invention,

FIG. 4 is a block diagram illustrating a power distribution arrangementin accordance with the invention, and

FIG. 5 is a view illustrating the transmission line and a connectingclip.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially to FIG. 1 of the accompanying drawings, a powertransmission line is illustrated which is suitable for use intransmitting power of a voltage between, for example, 150 volts and 1kv, at an operating frequency of greater than 10 kHz, most preferably ata frequency of 60 kHz. The power transmission line comprises twoprincipal conductors 1, 2. Each of the conductors is of substantiallyflat or rectangular cross-section, with two opposed parallel flat faces.The conductors may be formed of copper or copper alloy and may have athickness of between 0.025 and 0.25 mm, and a width of up to 30 mm,depending upon the current to be carried.

The two conductors are separated by a sheet of insulating material 3.The insulating material may be an appropriate plastic such as apolyester, polypropylene or polyphenylene sulphide. The thickness of theinsulating sheet 3 depends upon the voltage to be carried by theconductors 1 and 2 and may typically be of the order of 0.1 millimeters.

It is to be observed that the insulating sheet 3, in the embodimentillustrated in FIG. 1, has such a width that it extends beyond theconductors 1 and 2.

Although a suitable transmission line may comprise simply the threelayers described above, in this embodiment a foil 4 is associated withthe conductor 2. The foil 4 is made of a material having a high relativepermeability. Typically the relative permeability of the foil may be ofthe order of 10⁵. The foil 4 is secured to the face of the conductiveelement 2 which is remote from the insulating layer 3. The foil 4 has awidth which is greater than the width of the conductive element 2, sothat parts of the foil project beyond the conductive element 2 on eachside thereof.

The foil 4 may be formed from an amorphous or nano-crystalline metal,such as steel or a cobalt/steel alloy. Such a metal has a highresistivity.

Typically, a foil of high permeability of this type may be created byquench cooling molten metal at a very high speed, for example, at aspeed of 10⁶ degrees celsius per second. The molten metal may be sprayedonto a cooled, rapidly rotating drum. The metal cools on the drum andmay be removed from the drum in the form of a strip.

It has been found that the foil 4, or high relative permeability,constitutes a low reluctance path for magnetic field and, when adistribution line, as illustrated in FIG. 1 is utilized, on the side ofthe transmission line where the foil is provided there is a 100 foldreduction in the flux that causes radio frequency interference ascompared with an equivalent transmission line without a foil ofrelatively high permeability. On the other side of the transmission linethere is a ten fold reduction in the flux compared with an equivalenttransmission line without a foil of relatively high permeability.

The embodiment of FIG. 1 may be altered by providing a second foilcorresponding to the foil 4, the second foil being secured to theexposed faced of conductor 1.

FIG. 2 illustrates a second embodiment of the invention in which theconductors 1 and 2 are as described above, with the insulating layer 3being of the same width as that of the conductors 1 and 2. In thisembodiment, a foil 4 of high permeability material is provided incontact with the conductor 2, but has the same width as the width of theconductor 2. A second foil 5, of high permeability material, whichcorresponds directly with foil 4, is connected to the conductor 1.

It is found that by providing a foil of high relative permeabilityadjacent each of the conductors 1 and 2, the flux that generates radiofrequency interference signal is reduced, on each side of thedistribution line, by a factor of approximately 1,000. In the embodimentof FIG. 2 the foils have the same width as the width of the conductors.This provides a transmission line which is easy to handle, and which, ifdesired, may be easily provided with an insulating sheath. However,because the foils 4 and 5 do not extend beyond the conductors, theshielding effect provided by the foils 4 and 5 is not as great as itwould be if the foils 4 and 5 were wider than the conductors 1, 2.

FIG. 3 illustrates a further embodiment of a transmission line. In thisembodiment of the invention, the copper conductor 1 is provided as acentral core region 10 which extends axially of the transmission lineand, on either side thereof, two further spaced apart regions 11, 12,extend in parallelism with the core region 10. Similarly the conductor 2comprises a central core region 13 and, on either side, two furtherspaced apart regions 14, 15. The conductors 1 and 2 are separated by aninsulating layer 3. The conductor 1 is separated from a foil 5 of highpermeability by a thin insulating layer 16. Likewise, the conductor 2 isseparated from the foil 4 by means of a thin insulating layer 17. Thespaces between the various parts of each conductor 1 and 2 may be filledwith an adhesive such as an acrylic adhesive.

The entire arrangement, as so far described, is covered by an outersleeve 18 of an appropriate insulating material, such as a plasticmaterial.

It is to be appreciated that in the transmission line of FIG. 3, thelayers of foil of high permeability material are separated from theconductive layers, with which they are associated, by means of arespective thin layer of an insulating material.

It is to be appreciated that in the transmission line of FIG. 3, eachconductive layer is formed of a central core and further componentswhich extend parallel with that core but spaced therefrom. The provisionof an arrangement of this type has been found to reduce eddy-currentswhich might otherwise occur at the edge of a relatively large flatconductive core. The provision of an adhesive between the variouscomponents of the conductive element help ensure that the various layersthat form the laminate, that constitutes the distribution lineillustrated in FIG. 3, remain in a predetermined position relative toeach other.

It has been found that distribution lines of the type described aboveprovide very low inductance, low resistance and high capacitance. Thecapacitance provided by the distribution line can be incorporated intothe circuit of a power generator which is utilized to supply powerthrough the distribution line, for example as part of a resonatingcircuit.

It is preferred to use an appropriate insulating material for theinsulating sheet 3 between the conductors 1 and 2 so that thecapacitance is of a high quality, that is to say with a low power loss.The polyester material mentioned above provides good characteristics andis suitable for use at a low to medium temperature. Polypropyleneprovides better characteristics, but is only suitable for use at lowtemperatures. Polyphenylene Sulphide provides good properties, and issuitable for use at high to medium temperatures.

Referring now to FIG. 4 of the accompanying drawings, a powerdistribution arrangement in accordance with the invention isillustrated.

Referring to FIG. 4, a mains supply 20 is connected to a power factorcorrector 21. The power factor corrector is intended to ensure that thepower factor of the current drawn by the load is appropriate. In thisembodiment of the invention the power factor corrector is a rectifierwhich produces a 340 volt DC output.

The output of the power factor corrector 21 is provided to a highfrequency inverter 22. The output of the high frequency inverter 22 istypically 10 kHz or greater. The preferred frequency is 60 kHz. Theoutput of the inverter 22 is connected to a transformer 23 which must beconsidered to be “optional”. The transformer 23 may provide an isolatingfunction, separating, electrically, the components now to be described,from the components described above. The transformed may step the outputvoltage, provided by the inverter 22, either up or down, as is desired.

The output of the transformer 23 is connected to a transmission line 24.The transmission line 24 may have the form as illustrated, for example,in FIG. 1, FIG. 2 or FIG. 3 and as described above.

The two conductors 1, 2 of the power distribution line 24 may beconnected, as illustrated, directly to a load 25. The load 25 maycomprise an appropriate incandescent lamp, or could comprise a heater orsome other equivalent device.

A transformed 26 may have a primary winding connected to the twoconductors of the distribution line 24. The secondary winding of thetransformer may be connected to a load 27. Because the alternatingcurrent present on the distribution line 24 has a high frequency, inexcess of 10 kHz, the transformer need physically only be very small.The load may comprise, for example, a 12 volt dichroic incandescent lampor, alternatively, a discharge lamp. Of course, in the case of adischarge lamp, an appropriate impedance, such as an inductance willneed to be incorporated within the circuit to act as a ballast.

Alternatively, one conductor of the distribution line 24 may beconnected by means of an inductor 28 to a load 29, the other conductor,in the distribution line 24, being connected directly to the load. Theload may comprise a discharge lamp. The inductor 28 provides anappropriate ballasting effect.

While only one load connection of each of the three types discussedabove is provided, it is to be understood that a power distributionarrangement in accordance with the invention may supply power to a largenumber of loads.

FIG. 5 illustrates a transmission line 3 of the types shown in FIG. 2. Aclip 32 is provided which has two spaced apart blades 33, 34, whichengages the opposed faces of the transmission line. Although the highpermeability foils 4 and 5 are amorphous and thus have a highresistance, nevertheless, since the blades 33, 34 of the clip 32 engagea substantial area of the foils 4 and 5, the arms of the clip mayprovide an appropriate power-take-off. The arms of the clip may beconnected to, for example, a housing 35 which contains an appropriatetransformer for an item which is to be supplied with electrical power.Thus, a clip as shown may establish the connection between a load and adistribution line.

In an arrangement as described, the electric power is distributed at ahigh frequency. Problems that might arise, in connection with the use ofa high frequency distribution system, as a consequence of“interference”, are overcome by use of the specific transmission linewhich incorporates two substantially flat conductors which are locatedin spaced parallelism, very close to each other, and which are separatedby an appropriate insulator. The problem of interference may be reducedfurther by providing the high permeability material mentioned above.

The power may be distributed at a moderate voltage, for example, 300-340RMS, or 150-170 RMS or approximately 85 RMS. If the power is distributedat a moderate voltage, and needs to be transformed to a lower or highervoltage at the point of utilization, only a physically small transformerneed be utilized, because of the high frequency.

It has been found that in utilizing a preferred embodiment of theinvention, it is possible to connect a mains supply 20, through anappropriate power factor corrector 21, to a high frequency distributionsystem with a plurality of lamps being connected to the distributionsystem and each lamp being associated with its own electronic ballast.Because the lamps are provided with high frequency alternating current,ballasts need only be small and light. If the lamps are discharge lamps,it is possible to obtain high efficiency and substantiallyflicker-free-light. The power factor corrector satisfies the appropriatelegislation, and because a distribution line of the type described withreference to FIG. 1, 2 or 3 is utilized, there is virtually no H-fieldinterference

If the voltage present on the two conductors of the distribution line isalways equal and opposite, about earth, that is to say if the twoconductors of the distribution line are provide with an alternatingvoltage in anti-phase about earth, then only a very small electricfield, E, is generated.

In the described embodiment, a main supply is connected through a powerfactor corrector to a high frequency inverter to generate the initialhigh frequency. However, in alternative embodiments of the invention ,the high frequency may be generated directly from the mains using anappropriate frequency generator.

What is claimed is:
 1. An electric power distribution arrangementcomprising a source of alternating current having a frequency of 10 kHzor greater, a distribution line connected to said source, thedistribution line comprising three layers constituted by two conductors,each of substantially flat configuration with two opposed parallel facesand lying in separate planes, a first of said conductors lying in oneplane and a second of said conductors lying in another separate plane inspaced parallelism with said first conductor, the conductors beinglocated in spaced parallelism relative to the parallel faces and beinglocated a short distance apart, and an insulator that separates the twoconductors disposed between the two opposed parallel faces of the twoconductors of substantially flat configuration, at least one of theconductors included in the three layers of the transmission line beingassociated with a respective further element formed of a material ofhigh relative permeability, that element comprising a foil secured to aface of the at least one conductor remote from the insulator, thearrangement further comprising at least one load connected to saidconductors to receive electric power therefrom.
 2. An arrangementaccording to claim 1 wherein the at least one load is connected directlyto the two conductors.
 3. An arrangement according to claim 1 whereinthe at least one load is connected to the conductors by means of atransformer, the transformer having a primary winding connected to thetwo conductors, and having a secondary winding connected to the at leastone load.
 4. An arrangement according to claim 3 wherein the at leastone load comprises a discharge lamp, an impedance being provided whichis connected in circuit with the secondary winding and the dischargelamp.
 5. An arrangement according to claim 1 wherein the at least oneload comprises a low voltage incandescent lamp.
 6. An arrangementaccording to claim 1 wherein the at least one load comprises a dischargelamp connected to one of the conductors of the distribution line bymeans of an inductance and connected directly to the other conductor ofthe distribution line.
 7. An arrangement according to claim 1 whereinthe source of alternating current comprises a power factor correctorwhich receives supply from a main electricity supply, and an inverterwhich receives power from the power factor corrector.
 8. An arrangementaccording to claim 7 wherein the power factor corrector comprises arectifier producing a DC output, the DC output of the power factorcorrector being provided as an input to the inverter.
 9. An arrangementaccording to claim 1 wherein a transformer is provided between thesource of high frequency current and the distribution line.
 10. Anarrangement according to claim 1 wherein the further element formed of amaterial of high relative permeability extends laterally beyond the twoconductors.
 11. An arrangement according to claim 1 wherein the furtherelement formed of a material of high permeability is formed of anamorphous or nano-crystalline metal.
 12. An arrangement according toclaim 1 wherein the insulator separating the conductors comprises asheet of insulating material.
 13. An arrangement according to claim 1wherein the foil is separated from the face of the at least oneconductor to which it is secured by means of an insulating layer.